A number of modern electrical systems utilize components having disparate structural or operational characteristics—such as differing power supplies or operational voltage levels. Many consumer products rely on battery power or some combination of battery and continuous power supplies. In many cases, various electrical components and devices within such products have operational parameters that are not directly compatible with power from a battery supply. Frequently, therefore, systems that utilize some form of battery power require conversion of the battery output to levels compatible with the operational characteristics of a system's constituent components.
Consider, for example, automotive electrical systems—which can have a wide range of relatively high operational voltage levels. Standard operating conditions in such applications can run from, for example, on the order of 10 V-40 V, and in some fault conditions, those voltage levels could reach as high as 100 V. In contrast, the operational voltage range most high-volume commercial integrated circuit technologies operate with voltage supplies in the range of about 1.8 V-5 V.
In a number of instances, therefore, devices designed for use in such high voltage applications can not be produced in the most cost-efficient production technologies. For semiconductor devices, more robust and much more expensive high-voltage process technologies may need to be utilized. Additionally, or alternatively, lower voltage components may be supplemented with costly discrete components to compensate for voltage differentials. In either case, these measures result in a more costly or complicated design.
In a number of applications, switching regulator devices are employed to address voltage level mismatches. Switching regulators are one approach to providing dc-dc power conversion. Generally speaking, a switching regulator may comprise some form of inverter circuit connected to a low-pass filter, composed of an inductor and a capacitor. The inverter circuit produces a voltage waveform having on-time during pulses and off-time between pulses. The low-pass filter smoothes the waveform, thereby producing a constant dc voltage level. During on-time, the capacitor charges, and it discharges during off-time. Voltage level is regulated by controlling the duration and frequency of voltage pulses produced (i.e., on-time versus the off-time).
The ratio of on-time versus the total time for both on-time and off-time is referred to as the duty cycle. By lowering duty cycle, voltage is lowered—since charge-up time for the capacitor is shortened and discharge time is lengthened. Increasing the duty cycle increases the voltage—since charge-up time is lengthened and discharge time is shortened.
Common forms of conventional switching regulators use transistors as switches in an inverter network. The switches are turned on and off by providing a current or a voltage to the transistors' gates. The frequency with which such a transistor is turned on and off is controlled by a pulse-width modulator (PWM). Commonly, conventional switching regulators monitor peak current across some “sense” circuitry (e.g., across a resistor), and adjust output voltage from the transistor accordingly.
While this approach may be sufficient for some applications, there are a number of applications that require a regulated output current in addition to or instead of regulated output voltage. Consider, for example, certain automotive LED components and drivers. A number of such devices either require or operate optimally at a constant current level—notwithstanding variations in voltage levels elsewhere in the electrical system. Conventional switching regulators commonly do not address such a need or requirement.
Depending upon the particular regulated current needs of a given application, conventional switching regulators might be supplemented with discrete components to provide needed current regulation in a high input power setting. In some cases, such supplementation may be unsuccessful, or marginally effective. Even where such supplementation may be successful, the additional components can represent a substantial cost increase to the system.
As a result, there is a need for a system that provides versatile switching regulators compatible with use in high power input applications—and capable of providing current mode switching regulation—in a cost-effective, commercially-viable manner.